Particles "Numbered" Incorrectly When Generation Time is Influenced by Texture #80691

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Jonathan Manton · 2020-09-11T11:18:40+02:00

Jonathan Manton commented

2020-09-11 11:18:40 +02:00

System Information
See attached - probably not relevant.

Blender Version
Broken: 2.90 - see attached

Short description of error
A keyed particle system sends particles from one particle system to another particle system. Normally the ordering is respected: the first-generated particle in one system gets sent to the first-generated particle in the second system, same for the second-generated particle, and so forth. This does not work though if a texture is used to generate a particle system. Various visual effects rely on the ordering being respected.

Exact steps for others to reproduce the error
Create a plane mesh. Add a particle system to it, physics none, starting at time 1 and ending at time 10 with 10 particles. Add a blend texture so the particles are generated from one side to another. Add a second particle system on a second object. Now create a keyed particle system on the second object going from the first particle system to the second particle system, starting at time 15 and ending at time 24 with 10 particles. Display its particles in a distinct way (e.g., as red spheres). Step through the simulation frame by frame. Note the order that the particles appear on the plane mesh (first particle system). Then at frames 15, 16 and 17 note the order in which the keyed particles appear. They appear in a different order, whereas, if a texture is not used but the random seed is used, the keyed particles will be created in the same order that they were created in the first particle system regardless of the chosen random seed.

system-info.txt
Particle Numbering Bug.blend

**System Information** See attached - probably not relevant. **Blender Version** Broken: 2.90 - see attached **Short description of error** A keyed particle system sends particles from one particle system to another particle system. Normally the ordering is respected: the first-generated particle in one system gets sent to the first-generated particle in the second system, same for the second-generated particle, and so forth. This does not work though if a texture is used to generate a particle system. Various visual effects rely on the ordering being respected. **Exact steps for others to reproduce the error** Create a plane mesh. Add a particle system to it, physics none, starting at time 1 and ending at time 10 with 10 particles. Add a blend texture so the particles are generated from one side to another. Add a second particle system on a second object. Now create a keyed particle system on the second object going from the first particle system to the second particle system, starting at time 15 and ending at time 24 with 10 particles. Display its particles in a distinct way (e.g., as red spheres). Step through the simulation frame by frame. Note the order that the particles appear on the plane mesh (first particle system). Then at frames 15, 16 and 17 note the order in which the keyed particles appear. They appear in a different order, whereas, if a texture is not used but the random seed is used, the keyed particles will be created in the same order that they were created in the first particle system regardless of the chosen random seed. [system-info.txt](https://archive.blender.org/developer/F8864790/system-info.txt) [Particle Numbering Bug.blend](https://archive.blender.org/developer/F8880378/Particle_Numbering_Bug.blend)

Jonathan Manton commented

2020-09-11 11:18:40 +02:00

Added subscriber: @jmanton

Germano Cavalcante commented

2020-09-14 20:57:36 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-09-14 20:57:36 +02:00

Can you provide a simple .blend file showing the problem?

Jonathan Manton commented

2020-09-15 02:28:12 +02:00

Have uploaded a simple .blend file to the original submission. Also clarified the description of how to reconstruct the problem.

Richard Antalik commented

2020-09-16 12:01:09 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Jacques Lucke commented

2020-09-16 12:47:25 +02:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2020-09-16 12:47:25 +02:00

This is a limitation of the particle system. Each particle has an index assigned to at the very beginning, this index is only loosely related to the time the particle is born. Normal emission without texture would just spawn particles in order of the indices, but when using a texture, the order is changed. There should be ways to fix this of course, but it is unlikely that they will be implemented before we have a new particle system...

Philipp Oeser removed the

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Particles "Numbered" Incorrectly When Generation Time is Influenced by Texture #80691